
interface Arr {
  [index: number]: string
}

const arr1: Arr = []
const arr2: Arr = []

type Arr1 = string[]
const arr3: Arr1 = []
const arr4: Arr1 = []

type Num = 1 | 2 | 3
let num: Num = 1
// num = 4 // 报错